In the field of a refrigeration and air conditioning device, from the viewpoint of conservation of the global environment, an alternative refrigerant having a lower environmental load and higher efficiency has been demanded. In particular, CFC (chlorofluorocarbons) or HCFC (hydrochlorofluorocarbons), which has been used for a longtime is rapidly converted to HFC (hydrofluorocarbons) for preventing the destruction of the ozone layer or global warming. As the performance of such an alternative refrigerant, in addition to a low environmental load, high energy efficiency, low toxicity, low inflammability, etc. are required.
Since the 3rd Conference of the Parties to the United Nations Framework Convention on Climate Change (COPS), R410A has begun to be used for room air conditioners, package air conditioners, etc., and also, HFC134a (1,1,1,2-tetrafluoroethane) has begun to be used heavily for car air conditioners. R410A is a mixed refrigerant of 50 mass % HFC32 (difluoromethane) and 50 mass % HFC125 (pentafluoroethane), and is said to have a global warming potential (GWP) of 2088. Further, HFC134a is said to have a GWP of 1430.
However, in the European Union (EU), the mounting of a car air conditioner using a refrigerant having a GWP exceeding 150 has been prohibited since 2011, and so on, and there is a possibility of further expansion of the regulations. Therefore, recently, studies of new alternative refrigerants substituted for R410A and the like have been accelerated. As the candidate for the alternative refrigerant, single refrigerants such as HFC32 (difluoromethane), HFO1234yf (2,3,3,3-tetrafluoro-1-propene), and HFO1234ze (trans-1,3,3,3-tetrafluoropropene), and mixed refrigerants formed by a mixed composition thereof are exemplified.
In a compressor provided in a refrigeration and air conditioning device, a refrigerator oil is used. The refrigerator oil plays various roles such as lubrication of a sliding section, cooling of an electric motor, and hermetical sealing of a refrigerant inside the compressor. However, when the compatibility between the refrigerator oil and the refrigerant is low, the refrigerator oil and the refrigerant are not sufficiently mixed with each other, and a refrigerator oil phase and a refrigerant phase are separated from each other. Then, the refrigerant separated from the refrigerator oil locally prevents the contact between the refrigerator oil and the sliding section. As a result, appropriate lubrication by the refrigerator oil is not performed, and the durability of the compressor may be deteriorated.
Further, part of the refrigerator oil is vaporized or is turned into airborne droplets inside the compressor, and comes outside the compressor along with the refrigerant and circulates in a refrigeration cycle. When the compatibility between the refrigerator oil and the refrigerant is low, the refrigerator oil aggregates inside a pipe or the like, and is retained in the refrigeration cycle. Then, the amount of the refrigerator oil returning to the compressor is decreased, resulting in deterioration of the function of the compressor due to the decrease in the amount of the refrigerator oil. Further, the refrigerator oil retained in the refrigeration cycle sometimes prevents the circulation or heat exchange of the refrigerant. As a result, the efficiency such as COP (Coefficient Of Performance) of the refrigeration and air conditioning device is decreased. Therefore, when converting the current refrigerant to an alternative refrigerant, also the refrigerator oil to be used in combination with the refrigerant is required to be converted to an appropriate type.
Conventionally, as the refrigerator oil suitable for use in combination with HFC32 (difluoromethane), a refrigerator oil containing a polyol ester as a base oil is known. PTL 1 describes that an ester-based oil composed of a reaction product of at least one type of neopentyl polyol selected from pentaerythritol, dipentaerythritol, tripentaerythritol, trimethylolethane, trimethylolpropane, and neopentyl glycol and at least one type of aliphatic carboxylic acid selected from linear or branched chain aliphatic carboxylic acids or one type or a plurality of types of esterifiable derivatives of such an acid is used as a lubricant.
The environmental performance of the refrigeration and air conditioning device can be improved by adopting an alternative refrigerant having a low GWP such as difluoromethane. Moreover, the alternative refrigerant having a low GWP generally tends to have a high latent heat, and therefore, when difluoromethane is adopted as the alternative refrigerant, the amount of the refrigerant to be enclosed in the refrigeration and air conditioning device can be reduced. Then, by reducing the amount of the refrigerant, the diameter of a pipe or the like provided in the refrigeration and air conditioning device can also be reduced.